This invention relates to methods and apparatus for encrypting (and decrypting) signals, particularly video signals, and is suited especially for use in cable and satellite video transmissions.
There exists a need for secure encryption of video signals, such that only designated users may decrypt and display the information.
In typical encryption systems, one or more parameters of the signal to be encrypted are modified according to a pattern which is determined at the transmitter. The pattern generally is a member of a large class of similar patterns, such that discovery of the pattern through exhaustive search is extremely unlikely. A precise description of the pattern used for encryption is delivered to designated receivers, which then are able to recover the original information. The description of the pattern is known conventionally as the `encryption key`. The process of informing designated users of the encryption key is known conventionally as `key distribution`.
This invention relates to the choice of parameters of the original video signal to be encrypted, and to the techniques and apparatus for implementing the encryption and decryption at low cost. The problem of key distribution is not dealt with herein. Conventional and well-known key distribution techniques can be employed.